This invention generally relates to ram air turbine power systems (RATPS) that can be deployed to utilize energy from a passing air stream of a moving aircraft to generate hydraulic and/or electrical power. More particularly, the present invention relates to improvements of a RATPS which facilitate ground-level testing and ease of maintenance of the RATPS.
Many commercial aircraft are equipped with a RATPS. They are important elements in a spectrum of devices used to enhance aircraft safety. Typically, a RATPS is attached to a pivotal strut. During normal operation of an aircraft, the RATPS is held in a stowed position within an enclosed storage bay. In the event of a failure of an electrical or hydraulic power system, the RATPS is moved into a deployed position by opening the storage bay and pivoting the strut on which the RATPS is attached. In a deployed position, a ram air turbine is exposed to an air stream outside the aircraft. The ram air turbine drives a generator and/or a hydraulic pump to provide requisite power for control systems.
A RATPS is only rarely deployed as a matter of operational necessity. Indeed, during the past decade, there may have been only a dozen incidents in which in-flight power failure has required deployment of a RATPS on a commercial aircraft. Nevertheless, it is important to assure that the RATPS is always in a state of operational readiness. The determination of operational readiness is made by periodic testing of the RATPS.
Periodic testing has heretofore been accomplished by intentionally deploying the RATPS while an aircraft is in normal flight. There are inherent risks associated with in-flight testing. It is obviously safer to perform on-ground testing of any safety device. But, in the prior art, a typical RATPS has not been amenable to on-ground testing. A RATPS will only operate when exposed to high velocity air flow associated with a moving aircraft. Consequently, the more risky in-flight testing has generally been used as a standard procedure for assuring operational readiness of the RATPS.
Maintenance of most prior art RATPS's has heretofore been a costly and complex procedure. This is because a typical prior art RATPS is constructed as an integrated combination of a turbine, electrical generator and a hydraulic pump, with both the generator and the pump having their own separate reduction gearing. Consequently, it has been impracticable to remove just a defective pump from a RATPS without a complete disassembly of the turbine, reduction gearing and the generator. Similarly, a defective generator can only be replaced by performing a complete disassembly of the RATPS.
This maintenance difficulty is partially mitigated in a prior art RATPS disclosed in U.S. Pat. No. 4,742,976 issued to Cohen. In the Cohen RATPS, shown as a second embodiment in the subject patent, a hydraulic pump is attached to a flange of a gearbox. A generator is attached on an opposite side of the same gearbox. In this configuration, both the hydraulic pump and the generator are driven by the same rotating shaft. This arrangement facilitates easy replacement of either the pump or the generator. However, both the generator and the pump are driven at the same rotational speed in this arrangement. Consequently, the generator and the pump are both driven at a compromised speed. Neither the generator nor the pump is driven at its respective optimum speed.
As can be seen, there is a need for a RATPS that can be readily ground tested. Additionally, it is important that individual components, such as a generator or a pump of the RATPS, can be expediently replaced. It is desirable that such a system provides optimized rotational speeds for both a generator and a hydraulic pump.